This invention relates to light-emitting devices driven by an electric field and which are commonly referred to as electroluminescent devices.
Conjugated polymer based light-emitting devices have become a topic of great interest since the report of electroluminescent properties in poly(phenylene vinylene) (PPV). A large variety of polymers, copolymers, and their derivatives have been shown to exhibit electroluminescent properties. The configurations of these devices may consist of a simple single layer, bilayers, or blends used to enhance efficiency and tune the emission wavelength, or multilayers that may allow the device to operated under an applied voltage.
Typical single layer polymer LEDs are constructed by sandwiching a thin layer of luminescent conjugated polymer between two electrodes, an anode and a cathode, where at least one electrode is either transparent or semi-transparent. In some multilayer devices, charge injection and transport layers may be incorporated to improve device performance. A typical polymer LED fabrication process starts from a single indium-tin oxide (ITO) coated substrate, where the ITO acts as the anode. After careful cleaning, the polymer layers are then sequentially coated onto the substrate, usually by spin-casting techniques. Finally, a low work function metal is formed on top of the polymer layers by vacuum deposition techniques such as thermal evaporation or sputtering. This method of producing polymer LEDs has proven to be costly for large area applications.
Conjugated polymer light emitting devices offer substantial advantages over their inorganic counterparts such as solution processibility, easy band gap tunability, and mechanical flexibility. One unique advantage of conjugated polymer LEDs is their potential for web based roll-to-roll processing, whereby the cost of manufacturing polymer LEDs for large area applications can be significantly reduced. In the past few years, polymer LEDs have made remarkable progress toward commercialization. The effort, however, has been mainly focused on small area applications.
It is thus an object of the present invention to provide a method of fabrication that provides a fast, inexpensive means of fabricating polymer light emitting devices suitable for large area applications.
Although described with respect to the field of light-emitting devices driven by an electric field, it will be appreciated that similar advantages of lamination used in fabricating polymer devices, as well as other advantages, may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes methods for fabricating electroluminescent polymer devices and electroluminescent polymer systems by lamination. The methods of the present invention may be used in fabricating unipolar LED devices, bipolar SCALE devices and bipolar two-color SCALE devices. The methods of the present invention may be applied using procedures and protocols known and used in the arts to which they pertain. The present invention may be used to upgrade, repair, or retrofit existing machines or instruments using those aspects of the invention, using methods and components used in the art.
In broadest terms, the method of the present invention for fabricating polymer light emitting devices by lamination comprises: (1) obtaining a first member, where the first member includes a layer of a first electrode material, and a second member, where the second member includes a layer of a second electrode material; and at least one of said first and second members contains a layer of a light-emitting material capable of functioning as a light-emitting layer in a light-emitting device; and (2) laminating the first and second members so as to produce a laminate having said at least one light-emitting material between the first and second electrode materials. Either the first or second member, or both, may contain a layer of polymer selected from the group consisting of conducting and semi-conducting polymers, such as polyanilines, polythiophenes, polypyrroles, their derivatives, coploymers and blends thereof, and may also contain an outer layer of substrate material. The substrate material may be substantially impermeable to either oxygen or water. The substrate may be transparent. Further, the substrate may be rigid, resisting deformation from forces exerted by the human hand, or flexible, easily deformed by hand force. The laminate may comprise opposing electrical contact surfaces of the first and second members, and may be conducted such that at least one area of the laminate is sufficiently incompletely laminated such that the light-emitting device containing the laminate functions only upon application of pressure to the laminate. The laminate may alternatively comprise opposing electrical contact surfaces of the first and second member, where the opposing electrical contact surfaces are maintained in a spaced relationship by a layer of a spacing material in at least one area of the laminate, such that the light-emitting device containing the laminate functions only upon application of pressure to the laminate. The spacing material may be selected from the group consisting of aerogel materials and foamed materials.
The present invention also includes a method for preparing a layered composite capable of forming a light-emitting device comprising the steps: (1) obtaining a first member, where the first member comprises an outer layer of an electrode-bearing substrate material, and a second member, where the second member comprises an outer layer of an electrode-bearing substrate material; at least one of the first and said second members may comprise one or more layers of a light-emitting material capable of functioning as a light-emitting layer in a light-emitting device; and the inner side of either the first member and the second member, or both, comprises a polymer selected from the group consisting of conducting and semi-conducting polymers; and (2) laminating the first and second members so as to produce a laminate having said at least one light-emitting material between the first electrode material and the second electrode material. The conducting or semiconducting polymer may be selected from the group consisting of polyanilines, polythiophenes, polypyrroles, their derivatives, their copolymers and blends thereof, and the substrate material may be substantially impermeable to either oxygen or water.
The electrodes of the present invention may be patterned, such as for pixelation.
Examples of light emitting molecules that may be used in the emitting layer include: tris(8-quinolinolato)aluminum, bis(2-(2-hydroxyphenyl)pyridinato)beryllium, anthracene, tris(2-phenylpyridine)iridium doped in a host of 4,4xe2x80x2-N,Nxe2x80x2-dicarbazol-biphenyl, their derivatives and blends thereof.
Examples of light emitting oligomers that may be used in the emitting layer include: oligo(phenylenevinylene)s, sexithiophene, oligo(thiophene)s, oligo(pyridine)s, their derivatives and blends thereof.
Examples of light emitting polymers that may be used in the emitting layer include: poly(arylene vinylene)s, poly(phenylene)s, poly(fluorene)s, poly(vinyl carbazole), poly(pyridine), poly(pyridyl vinylene), poly(phenylene vinylene pyridyl vinylene), their derivatives, their copolymers and blends thereof.
The present invention also includes a method for preparing a layered composite capable of forming a light-emitting device comprising the steps: (1) obtaining a first member, where the first member comprises an outer layer of a substrate material, and a second member, where the second member comprises an outer layer of a substrate material; both the first and said second members comprise layers of a light-emitting material capable of functioning as a light-emitting layer in a light-emitting device; the substrate material of the first and second members comprises an electrode material substantially impermeable to either oxygen or water; and the inner side of the first and second member comprises a polymer selected from the group consisting of polyanilines, polythiophenes, polypyroles, their derivatives, their copolymers and blends thereof; and (2) laminating the first and second members so as to produce a laminate having said at least one light-emitting material between the first electrode material and the second electrode material.